In many work site applications of today, high-precision position of work machines, work vehicles, vessels, or work platforms is required, for example, at a marine or naval work site where a number of marine or naval work vessels and/or marine or naval work platforms perform work task at maintenance work of a submarine pipeline or submarine cable, or at a construction work site where earthmoving construction machines such as graders and dozers performs work task to construct a road. For example, in the civil engineering and construction industry of today more and more applications require high-precision position for earthmoving construction machines such as graders and dozers. Survey units or total stations are located on a work site for, inter alia, automatically tracking such construction machines by measuring a distance to the machine and providing the machine with positioning data. Such total station are, for example, described in WO 2004/057269 by the same applicant.
The surveying unit is based on optical surveying allowing the unit to follow a machine and also includes a built-in RF transceiver which provides two-way communication with the machines and a controlling computer thereby enabling the unit to provide a machine with, for example, position data.
During, for example, a road construction, it is important that the construction machines continuously are provided with accurate positioning data in order to give a predetermined topography to a specific place of ground. The desired topography for each position of the construction work site is written into a computer program stored in, for example, the controlling computer and may be provided to the machines in advance or continuously and automatically together with its position at the work site.
In general, several machines and several geodetic instruments or survey units are located on a work site and each machine communicates with one or several survey units, for example, by using a frequency hopping spread spectrum technology operated in the 2.4 GHz ISM band. In order to provide a reliable and accurate coverage of a complete work site, a large number of survey units are required to provide reliable and accurate machine control at the work site. The machines often move over different areas of the site, which only some of the units may access due to, for example, range limitations. In order to be able of continuously download position data, a machine may have to switch between different survey units during the operation. A survey unit that has been set in an idle mode by a machine normally starts looking after a new machine to communicate with. In a frequency hopping technique system each machine communicates with at least one station over a radio channel and a large number of radio channels may thus be used. Thereby, a survey unit may have to, in order to establish and initiate a communication session with a machine, search through all channels and it takes 5-10 seconds to gain lock to one hopping pattern. Thus, in case of 64 channels it may require 5-10 minutes to scan through all 64 channels.
Hence, there is a need of an improved and more efficient method for providing work vehicles, such as construction machines, work vessels, or work platforms, at a work site, such as a marine or naval work site, a construction work site, a building work site, a housing site or a mining work site, with real time position data from survey units or total stations located at the work site.